Art of storing or delaying the transmission of electrical signals



Aug. 10, 1954 M COHEN 2,686,275

ART 0F STORING OR DELAYING THE TRANSMISSION OF ELECTRICAL SIGNALS FiledMarch 31, 1951 INVENTOR Patented Aug. 10, 1954 UNITED STATES PATENTOFFICE ART F STORING 0R DELAYING THE OF ELECTRICAL TRANSMISSION SIGNALSMartin J. Cohen, Princeton, N. J., assignor to Radio Corporation ofAmerica, a corporation of Delaware 9 Claims.

This invention relates to improvements in the art of storing or delayingthe transmission oi electrical signals.

The prior art offers many examples of storage tubes of theelectro-mechanical and electrostatic varieties. Irrespective of theadvantages claimed for a given tube it may be said generally that itpossesses certain disadvantages inherent to its class. Thus, if thedevice is of the electromechanical variety, its ability to handleelectrical signals without distorting them is adversely affected by thenecessity of translating the signalsinto mechanical vibrations, and backagain. On the other hand, if a storage device is of the electrostatictype its ability to maintain a number of signals in storage is limitedby the leakage characteristics of the material (e. g. mica) upon whichthe signal-bearing electrostatic charges are stored.

Accordingly, the principal object of the present invention is to obviatethe foregoing and other less apparent objections to electro-mechanicaland electrostatic types of storage devices and to provide a novel,relatively distortionless, method of and apparatus for storingelectrical signals.A

Another object of the invention is to provide a storage device having anadjustable storage or delay time, and one capable of handling a multiplicity of discrete signals withouty cross-talk or leakage.

Stated generally, they foregoing and other objects are achieved inaccordance with the invention by producing small groups of ions, say atone end of a gas-filled tube, and then collecting the ion groups at theother end after they have travelled the length of the tube. The delaydue to the transit time of the ions, and consequently the memory ordelay time of the tube, depends upon the choice of operating parameterssuch as; applied voltages, nature and pressure of the transit medium,etc.y It may range from a fraction .of a second to several seconds, oreven longer if output signals are fed back into the input in acontinuous process.

The invention is described in greater detail in connection with theaccompanying single sheet of drawings wherein:

Fig. l is a longitudinal section of a storage device constructed inaccordance with the principle of the invention and including anevacuated gun-chamber and a gas-nlled storage chamber;

Fig. 2 is a longitudinal .section of the storage ory ionization chamberof the deviceof Fig. 1,

said' storage chamber containing analternative` form of outputelectrode-assem'bly';v

Fig. 3 is a side view of a tube, cut away in part to show a schematicpresentation of the electron gun, and a longitudinal section of theionization chamber which affords many simultaneous corridors ofinformation; and

Fig. 4 is a fragmentary View, partly in section, showing an alternativeoutput electrode assembly for the tube of Fig. 3.

The tube shown in Fig, l comprises a gas-tight envelope II divided intoa first chamber i3 and a second chamber I 5 by an hermetically sealed-inwall I 'l with an electron permeable window I9.

The Wall I1 is constructed of copper so that it may serve as anelectrode offering a conductive path to ground. The electron-permeablewindow I9 is of the Lenard type, i. e. it holds a vacuum but ispermeable to an electron beam. It may comprise a thin sheet of aluminumfoil. The first chamber I3 is evaculated and contains an electron-beamsource comprising: an electron emitter 2! a control electrode 23, and anaccelerating and focusing electrode 25. These members are so positionedthat the electron beam produced by them is directed toward the electronpermeable window I9. The second chamber I5 contains under pressure apure gas (argon is suitable), and has a collector electrode 2'! situatedat the opposite end from, andy directly in line with, the electronpermeable window I9. The pressure of the gas is in the neighborhood ofone atmosphere, but it may be varied over wide ranges consistent withother properties and functioning of the tube.

The electron beam from the iirst chamber i3 travels at suicient velocityto pass through the window I9 into the second chamber I5 and, byknocking electrons from their orbits within individual gas molecules,produces positive ions in the immediate vicinity of the Window i9. Theextent of this ionization is explained more fully below under theheading, Transit Time, Diffusion, etc. The electrons which the beamdrives out of the gas molecules are collected on the electrode I1, andthe resulting positive ions drift in a substantially straight paththrough the gas toward the collector electrode 21 under the influence oian electro-static eld set up by a source oi variable potential,represented by the battery 26, between the wall electrode I1 which .1 isat ground potential and the collector electrode 2l' which is at anegative 10,000 volts. The time that it takes these ions to completetheir transit through the gas depends upon variable factors and may becalculated by formula in a manner which will be more fully explainedbelow. It is this drift time which introduces into the tube the delaythat makes it useful as a memory device. The electron beam which createsthe ions in the chamber l5 is controlled by input signal voltagesapplied to the control grid 23 of the beam source in chamber I3.

Standard techniques are used to detect the arrival of ions at thecollector electrode 2l' and derive output signals therefrom, e. g.differentiating circuit external to the tube and not shown in thedrawing.

Instead of the single electrode shown in Fig. 1, Fig. 2 shows thecombination of a screen electrode 29 and a solid electrode Si as asignal pickup means. The screen electrode 29 is located slightly infront of the solid electrode 3l in the path of approaching ions. 'Iheoutput from the tube is taken across the resistance 42 in the circuitconnecting these two electrodes. This circuit includes a variable sourceof potential indicated by the 1000 volt battery lili which keeps thesolid electrode 3l more negative than the screen electrode 29. While theions are in the area between the electron permeable window I9 and thescreen electrode 29 there is no signal current in this circuit, but whenions pass through the region between the screen electrode 29 and thesolid electrode 3i current flows in the circuit between them and asignal voltage appears across the resistance 42.

The tube shown in Fig. 3 comprises an evacuated compartment 28 and agas-filled compartment 30. 'I'he evacuated compartment 28 has anelectron beam source comprising: an electron emitter 32, a controlelectrode 3G and an accelerating and focusing electrode 3E whichfunction in conventional manner to produce an electron beam 38. The twocompartments 28 and 30 are separated by a target electrode 33 whichcomprises a light-transparent supporting member 35 with a fluorescentcoating 3l on the side presented to the beam 38 and a photo emissivecoating 39 on the side presented to the ionizable gas. Deecting elements5,! associated with the evacuated compartment 28 cause the electron beam38 to scan the fluorescent surface 3l of the target 33.

Instead of the single collector electrode shown in Figs. 1 and 2, thistube has a plurality of collector electrodes 43. Six are shown but anyconvenient number may be used within limitations which are discussedbelow under the heading, Multiplicity of information.

As the electron beam 38 scans successive areas of the phosphor side 3lof the target electrode 33, it causes the phosphor immediately underelectron bombardment to give off light. This light passes through thetransparent supporting member 35 and when it arrives at the photoemissive side 39 of the target 33 it causes the photoemissive materialin that area to emit electrons which attach themselves to the gasmolecules in the immediate vicinity, thereby creating negative ions.These negative ions then drift in separate groups toward the collectorelectrodes 43 which are at a positive 10,000 volts with respect to thetarget electrode 33. As the electron beam 98 scans across the target 33,many such paths or corridors are activated. The maximum number ofcorridors available depends upon crosstalk due to lateral diffusion ofthe ionized gas. This lateral diffusion is discussed below under theheading, Multiplicity of information.

Because ions travel in a straight line toward the closest electrode ofopposite potential under the influences of a uniform potential eld, thistype of structure can be utilized to provide any number of corridors ofion travel and consequently of electrically stored information.

The field in which the ions travel is kept uniform by means of apotential gradient device 45 comprising alternate electricallyconducting rings 4l and resistance elements 49. The effect of thisdevice is to divide the potential drop between the target electrode 33and the collector electrodes 133 into even steps and keep straight thelines of potential gradient between the target 33 and the collectorelectrodes 43. The rings 41 are embedded into the walls of the chamber30 so that they have a surface exposed to the interior. An alternativemethod of securing an even distribution of potential is to coat theinner surface of the envelope with a high resistance conductivematerial.

rThe arrival of ions at the collector electrodes i3 may be detected by adiierentiating integrating circuit, as mentioned in connection with thedescription of Fig. 1. Alternatively, a take-off cathode ray beam may beused, as shown in Fig. 4. In the latter case, the electrically separateelectrodes 5i upon which the ions are collected are individually sealedinto the glass wall 53 of the gas-filled chamber with an exposed surfaceon each side of the wall. Sealed against this wall 53 is an evacuatedenvelope structure 55 containing an electron gun 5l, defiecting means 59and a signal electrode 6l. Following a known technique in the pickuptube art, the electron beam 62 travels from the gun 5l and bombards thetarget or wall 53 at a voltage above rst crossover. The eiect is toraise the potential of the elements 5| to that of the screen 6l (10,000volts). Once the elements 5l are so charged, the entire beam 62 isreflected back to the screen 0i. ts electron content is aflected by thenegative ion charges which have accumulated on the individual electrodes5|. In the circuit between the signal electrode 6l and ground is anoutput resistance Sli. The changes in electron content of the beam 62 asit is intercepted by the electrode 5i and conducted to ground causevoltage variations across the resistance 64 and become the signal outputof the tube.

Multiplz'city of information The amount of information which can bestored per electron beam in a tube of the type shown in Fig. 3 islimited by three factors: (a) the number of storage paths available, (b)the amount of information which can be stored in each path, and (c) thenumber of individual ion groups which the scanning electron beam canstart down the separate corridors of the tube during the transit time ofan ion between electrodes. In this specication the storage paths(separate parallel paths of ion travel) are referred to as corridors andeach time or space division capable of carrying information Within acorridor is termed a channel As previously mentioned, ions travel insubstantially straight lines to their collector electrodes makingpossible a great number of parallel corridors in a single tube. Onelimitation on the number of corridors which is practicable is a possiblelateral difusion of the ions in transit. This makes some physicalseparation between neighboring circuits necessary to prevent crosstalk.Co-axial magnetic iields (not shown) around the tube, or insulatingpartitions within the tube (also not shown) can be used to cut down onthe physical separation necessary between corridors. As demonstratedlater in the specification under the title, Transit .TimemDiiusiom etc.,however, even without the co-axial "elds and insulating partitionssuggestedabove, the physical separation .necessary to: prevent crosstalkis not too serious a limitation. In argon, for example, aanionwill;.cliff-usefoniy --.'036 cm. in .01 second which=is a vpracticabletransit time between electrodes.

The number of separate items of information '.'Whiohfican be writteninto a tube ofzthe type shown in Fig. 3 isa function of the transit, ordrift time, of an ion in the tube, and the scanning speed of theelectron beam which produces the ions. Theseparateitems can'vbeufwritten in separatecorridors or they .can be. channeled into 'avsingle, `or relativelyfew corridors. 'Inany 'event their number, iora'given scanning speed,

can be :calculated ,from the formula:

where n=the number of items of informationpossible. `t=thel transit timeof ions travellingbetween electrodes down a corridon (This `-`isttheeffective time available `for laying Vdown or =writing :signals l'in a.total number oiifcor- .;ridors, because there .is u no point iinihaving A.more corridors -than can Vvbe :used A.simultaneously.)

t=.'0l is selected asa-"desirable delay time. fw1=thettime it takesthe"fwritingelectron beam to ionize suflicient molecules of gas within acorridor` to produceasignal.

w1=025 106- is convenient to. (secure. a .satisfactory band width and.anamplesignalto-noise ratio at the collector electrode. It is alsoconsistentwithaasuitablessize for the instrument and accepted scanningtechniques. w12=the time intakes the'writingfelectron beam to traversethe .space between corridors (or the spacing betweenppulses within acorridor). w2=0-5 106 is selected as representative, if, :in order toget #adequatefseparationythe -space'between corr-idorsfr pulses) Iis toequal approximately'the .width of-la corridor, or *the time it takestowrite a signal.

When the values suggestedfabove.-arecapplied .to s theformula,

or .10,000 vpossible .items `of :information :If .the 10,000 .separateitems of informatien .referred to above .y are 'i to be carried inseparate corridors within the tubetthe question oi lphys-ical sizeof:the tube ,required arises, 'This question involves. such considerations'as the dian-ieterro'f the .ion lgroups `.as :they s are initially f'createdl'by the writing electron beam and the extent to which 'theydiffuse in transit .down fa corridor. The 4electron beamsspot area'`onfthe gtargetH33 maybe .assumedto be vapproximately i008 lsq.: cm. (CfSpangenberg, Vacuum .'Iubes, :page 11427..) 'As a. result, laniongroupfas itstartathrough the drift. mediuml is 5.008 It, as:issnientionedaabove, ions willrdiffuse. only `about .036vc1n. inalltr-ansit time/of :0l seconoLithen ilxsqcm. loi-=area wculiiprovideampie 'crossv section .to contain :a v:single corridor. 'Thiswould permit105000fdiierentfcor- Ariders to be carried with a marginofsaietyfin al2icm.: diameter i-tube. 'The num-ber of "foer- 6,f-ridorsavailablef'in-aztube of-.ia-givenidiameter ris a .f functionl.of the tubes icrossz-sectional xarea and may be calculated from theformula:

Number -of corridors available1,7%2

l.where r lis given.v in.. cmrandthe .Olis thearea ofr a, .1: cm. squarecorr-iden y.The -amounttoi .information 'which can .be ,channeiled intoeach .corridor.depends upon several factors. The first limitation fis-the transittime of the-iongroups through the tube. This ydetermines,how: much thetube can held Many-,given time. ,.But :Within this,periodxof transit time therer-mayf be a greatnumber .of pulses: ofinformation and each ion group can .represent -a separate channel of.information within its own corridor .If we-assurne a transit -tiine of.01.sec., a .great number is prac- ..tioable) of micro-,second .pulseswith .adequate Vspacing between .them to Aprevent interference can beutilized. .The spacinginust be sufieiently .Wide to take'careotdiiusionof the .ions in .transit toward the collector` electrode. .(Thisdiffusion problem is discussed below.)

A proper combination of corridors, and channels Within corridors makesit possible to store many times 10,000 different elements of binaryinformation. Furthermore, since the col- `lector electrode and itsassociated circuitry can bemade sensitive to the degree of amplitude ofa vpulse as well as to its mere presence, inter- -niediate informationas well as binary OIT-on Yconditions can be indicated and stored. 1t hasbeen explained. aboveihow`l`0g000 ^corridorsfcan be contained inaiigfcmxdiameterftube. @This .wou-ld.. call. lfor asoanning speed. of1.01 .secondper raster. By increasing the speed. offthescanning beam,however, ..so..that.. .it lays down. 1a succession of ion pulsesineachcorridor.bef.ore..the .rst ,pulse .has y.completed .r its `transit ytothe collector electrode, it..is.possi-ble to.multiplethese110,000corridors= by agreatnumber of. channels-within corridors The -numberofAchannels .possible within .a .single Ycorridor .is in .the .hundreds asshown in the chart. below. .Thus itis .conceivable that more than ainillioneleinents .of..information can be stored if .the writing beamscans fast 'enough to complete ia hundred `or 'more rasters during'theion'transititime. Asexplained above, this scanning time: isiimitedamongother`things fby'thetime necessary-to lgive each ion group-Janladecuiate signal to-'noise i ratio.

Trnsitftz'me, diffusion, etc.

(References: Cork, rRadioactivityY.and Nucleai-.Physics;

Loeb, Fundamental Processes of:ElectricaLDischargeiin Gases.)

When ions are produced I;by `bornbaniment throughafLenard window.' thedepth oi ionization is a function of the energy excess of the electronsafter they have penetrated Vthrough the diaphragm-of the window.'Anexcess'f2500 v. will ionize to a depth oi about .Ofi om. and' 1000 v.to about .003 om. (Rei. Cork). (A chart, onpage 293, vol. 4 of the RCAReview publication Television shows the percentage o1 available energyafter a cathode ray pierces a Lenardewindow as a function of windowthickness and beam voltage.) For each electron which penetrates into thegaseous region several electrons'and positive ions are formed, and theexcess energy (i. e. the energy above that which is necessary to 'piercethe window) is dissipated at arate oi approximately 30 electron voltsper ionizedpai-r. .These are the factors which along with the timeduragroups which can be channeled through its corridors.

As explained above, the depth of these groups is affected, not only bythe time duration of the electron beam which accomplishes theionization, but also by the degree to which that beam penetrates intothe gaseous region to be ionized. There is another factor which has aniniuence on the depth of the ion group as it passes through the gasfilled chamber. This is the tendency oi' the ionized gas molecules todiffuse gradually throughout the gaseous region. This tendency of gasions to diiuse must be taken into consideration in calculating theamount of information which can be channeled along any given (6).DL-.0235 K N-e) (8) N= i (using Equation 5)= 2x (ft Vc (using Equations2 and Equation 8 shows that the number of channels within a corridor isindependent of the size of the instrument and volume of the gas butincreases with the square root or" the voltage (V) between electrodes.'This is based on the assumption that the pulse has a width diffusionwidth upon formation.

The chart below shows the number of channels increasing V andapproximately at the rate N :2.9 V

(dividing Equation 2 by Equation 4) corridorf Voltage Distance TransitNo. of across between gds'g go/051,133 time, Cgtrn Chantube electrodes tsec. nels 0m. Mcrosec.

In performing these calculations the ollowing approach is helpful. Let:

the extent to which the input pulse has been widened by diffusion of itsion (assuming pulse of zero width at beginning). E is the distance thepulse is widened from the central aXis therefore the total widening is252-) Tim 3Jt 1 atm. pressure (k for argon-l.3 cin/sec.

volts/cm., with positive ions) (International Critical Tables, vol. 6,p. 111). D=difiusion parameter (.0235 k.) (Ref. Loeb supra).

d (2) 15:; (3) v=k Using the rst case stated in the chart the diffusionof an ion group in .0092 second is calculated as follows:

25;(f0r i=.oo92 sec.)

2(.19)(.o092)1/2=.036 cm.

Gases In the gas-lled tubes described above there are two diierent typesof ionization calling for two diierent types of gas.

In the first type (Fig. 1) ionization is accomplished by electronbombardment through an electron permeable window which bombardmentseparates electrons from the gas molecules to produce positive ions. Inorder to prevent the free electrons from combining with other moleculesof the gas to form negative ions, a gas is selected which has a smallco-efcient for electron attachment. (E. g. the probability of a freeelectron attaching to a molecule with which it collides is less than 105to one.) Some suitable gases are: the rare gases helium, neon, argon,krypton, xenon, hydrogen, nitrogen, carbon monoxide, and carbon dioxide.Ihe excess electrons are eliminated by attraction to the wall-electrodeIl.

In the second type (Fig. 3) ionization is accomplished by activating anelectron emitter which sends forth electrons to combine with individualmolecules of the gas to form negative ions. Here the situation isopposite to the above case where the object was to eliminate electrons.Instead, we want to add them to the gas molecules. So a gas is selectedwith a high co-enicient for electron attachment. (E. g. the probabilityof a free electron attaching to a molecule with which it colli'des ismore than i0-4 to one.) Considerable portions of the gas should be oneof the following: afhalogen, oxygen, waterovapor, hydrogen-- suln'de,ammonia,. andI nitrous oxide. Fior. the. secondftype ofoperation only,gasv selected .from the 1 above. may.. be. mixed withl one of the: gasessuggested for the..nrstv type. But it isrecoinmended that gaseswithinthe same.l group. should notib'e. mixed'zin .either type` of `'operationbecause this'. would result. inv ions .of f diierent gases. withdifferent.characteristics. .and .transit times..

The delays introduced in a device of the sort described are of the orderof a few seconds or fractions thereof. Longer memory may be achieved byrunning information back through the tube by means of associatedcircuitry connecting output to input. In this manner a signal may bestored indefinitely. rlhe ei'ects of diffusion are oiiset by appropriatecircuitry to sharpen the pulses each time they are fed back through thetube.

One of the corridors or given pulses within any of the corridors, can beutilized for synchronization or control purposes indicating when one ofthe parameters should be changed in order to operate the device at thedesired delay time. Thus voltage and temperature irregularities etc.,can be compensated for. Response to the indicated change can byappropriate auxiliary 'devices be made automatic.

The storage tubes and delay devices of the invention have been describedas feeding into differentiating circuits for deriving a signal output.It will be understood that they may also be fed into other types ofcircuits and used for other purposes, e. g. they can be used as countingdevices in cooperation with integrating circuits.

The invention has been presented as embodied in a gas lled dischargetube. The disclosure in this respect is to be interpreted as beingillustrative and not in a limiting sense. rThe ionizable medium maycomprise any iluid material wherein the elementary particles ormolecules are capable of changing their electrical chargecharacteristics (i. e. add r subtract an electron relatively easily).Among such ionizable media are dust particles in air, oil droplets invarious emulsions, etc.

What is claimed is:

l. A storage device for electrical signals comprising, an envelopecontaining an ionizable medium at a pressure of the order of oneatmosphere, a plurality of electrodes mounted to define the terminals ofa path in said ionizable medium, means for creating a signal-modulatedlocalizeddischarge in said ionizable medium adjacent to one of saidterminals, means for establishing a potential difference between saidelectrodes of an intensity and sign calculated to draw saidlocalized-discharge in a substantially straight path away from its areaof origin through said ionizable medium in the direction of said otherterminal electrode, means including said other terminal electrode forderiving signals from said signal-modulated localized discharge, and atleast one other electrode intermediate said terminals of said path.

2. The invention as set forth in claim 1 and wherein means are providedfor varying the potential-diiference between said terminal electrodes,whereby to regulate the transit time of said signal-modulated dischargethrough said ionizable medium.

3. The invention as set forth in claim 1 and wherein said means forcreating a signal-modulated localized discharge in said ionizable mediumcomprises an electron-gun.

4; The inventionzas.setorthinclaimil andi wherein said envelopecomprisesY an. electron?. permeable gas-tighty partition vrwhichdivides,` said;- envelope into. a gas-chamber and'. an.-` evacuatedchamber; and wherein said met-mentioned means` comprises a.grid-controlled .f electron-.gun mounted within said evacuated chamberin line with said eleotrora-permeableA partition..

5. An electrical delay-device comprising a gastight envelope having twochambers having a,l common gastight wall, an electron permeable windowin`said-wall5 a beam-source of electrons mounted in one of said chambersin a position to bombard said window, the other of said chamberscontaining a gas of a 'type and pressure capable or" localizedionization in response to the impress thereon of said electrons, acollector electrode in a part of said gas-lled chamber remote from saidelectron permeable window, and a foraminous auxiliary electrode mountedin the gaseous space between said window and said collector electrode.

6. The invention according to claim 5 wherein said ionizable fluidconsists essentially of a gas having a low coefiicient ofelectron-attachment.

'7. An electrical delay device comprising an envelope having atranslucent gas-tight partition 'dividing the interior thereof into anevacuated compartment and another compartment containing an ionizableuid, a beam source of electrons mounted in said evacuated compartment ina position to scan said translucent partition, an electron-sensitivephoto-emissive coating on the scanned surface oi said partition, aphoto-sensitive electron-emissive coating on the opposite surface ofsaid partition and within said other compartment, a plurality o1collector electrodes immersed in the ionizable uid in said othercompartment remote from said partition, means for establishing apotential diilerence between said partition and at least one of saidcollector electrodes of an intensity and sign calculated to draw alocalized-discharge in a substantially straight path away from saidpartition through said ionizable fluid in the direction of saidcollector electrodes, means including said collector electrodes forderiving signals from said localized discharge, and at least oneelectrode intermediate said partition and said collector electrodes.

8. The invention according to claim 7 and wherein said ionizable fluidconsists of gas having a high coeincient for electron attachment.

9. An electrical discharge device comprising an envelope containing twospaced apart gas-tight partitions dividing the interioi of said envelopeinto a central compartment and two oppositely located evacuatedcompartments, an ionizable huid in said central compartment, a beamsource of electrons mounted in each of said evacuated compartments in aposition to scan the adjacent surface of its partition, the scannedsurface of one of said portions comprising an electronsensitive,light-emissive coating, the opposite side of said partition having anelectron-emissive coating sensitive to the light emitted by said rstmentioned coating, the scanned surface of the other partition comprisinga plurality of discrete electrodes for collecting ions resulting fromthe release within said gas of electrons from said light sensitiveelectron emissive surface means for establishing a potential differencebetween said partition having said electron emissive coating thereon andat least one of said electrodes of an intensity and sign calculated todraw a localizeddischarge in a substantially straight path awayReferences Cited n the le of this patent UNITED STATES PATENTS Name DateNull Feb. 21, 1928 Number Number 12 Name Date Schroter et al June 11,1935 Applebaum Feb. 11, 1936 Barthelemy Aug. 11, 1936 Thomas Jan. 10,1939 Strubig June 6, 1939 Farnsworth Aug. 27, 1940 Lubszynski et a1 Oct.7, 1941 Ponte Dec, 4, 1951

